Wire arc spray system using composite wire for porous coating, and related method

ABSTRACT

A wire arc spray system use at least one first wire and second wire that include a composite wire including a first material at a core region thereof and a cladding including a second material surrounding the core region. A controller controls operation to propel heated material created by the arcing of the first wire and the second wire at the arc point to a surface to be coated. A wire arc spray methodology for creating a porous metal coating with all-metal wires is also provided.

BACKGROUND OF THE INVENTION

The disclosure relates generally to coating techniques and systems, andmore particularly, to a wire arc spray system using a composite wire forcreating a porous coating and a related method.

Metal abradable coatings include porous metal coatings and are used in avariety of industries. For example, metal abradable coatings may beapplied to an inside of a casing of a gas turbine or a compressor of ajet engine to create abradable seal coatings that act on moving parts tocreate precise tolerances for sealing. Currently, metal abradablecoatings are applied by plasma spray or combustion spray using powdersthat include a metal and a material that can be burned out such as apolymer (e.g., polyester) or other low melting point material. In somecase, a solid lubricant such as boron nitride is also employed. Thematerials that are burned out are some times referred to as fugitivephase material. Once the composite materials are applied to a surface,they are heat treated to burn out the of the fugitive phase materials,resulting in a porous, abradable coating of the metal material on thesurface. Another approach to creating metal abradable coatings is tobond the fugitive phase materials to the metal powder with a lowtemperature adhesive that will burn off during heat treatment. Abradablecoatings can be expensive to create due to the processes used andnon-portability of the equipment and materials used. The compositepowders used in the plasma spray process also suffer fromreproducibility problems and sole source limitations on the fugitivephase materials leading to expensive composite powder prices.

Wire arc spraying is another approach for coating a surface with a verydense, non-porous material. Porous metal coatings have, however, beenproduced from wire arc spraying by using a sacrificial metal wire, e.g.,of zinc, with a dissimilar metal wire, e.g., of nickel, andelectro-chemically etching out the sacrificial metal to leave porousmetal behind. This application generates porous metal advantageous for,e.g., fuel cell electrodes, but not abradable seal coatings. Wireshaving aluminum cladding and an alumina core have also been employed forcreating anti-skid coatings. In this case, the alumina does not melt(melting point 2072° C.) with the aluminum (melting point 660.32° C.)and is not removed, but is trapped in the coating, resulting in a veryhigh surface roughness.

Other efforts to create abradable coatings generate complex honeycombstructures on the surface with various fillers in the cells.

BRIEF DESCRIPTION OF THE INVENTION

A first aspect of the disclosure provides a wire arc spray systemcomprising: a propelling gas source for delivering a propelling gas toan arc point; a first wire delivery apparatus for delivering a firstwire to the arc point; a second wire delivery apparatus for delivering asecond wire to the arc point, wherein at least one of the first wire andthe second wire includes a composite wire including a first material ata core region thereof and a cladding including a second materialsurrounding the core region; a source of the first wire positioned toprovide the first wire to the first wire delivery apparatus; a source ofthe second wire positioned to provide the second wire to the second wiredelivery apparatus; an electrical source for creating a first electricalpolarity in the first wire and a second electrical polarity that isopposite to the first electrical polarity in the second wire; and acontroller for controlling the electrical source, the propelling gassource and the first and second wire delivery apparatuses to propelheated material created by the arcing of the first wire and the secondwire at the arc point to a surface to be coated.

A second aspect of the disclosure provides a composite wire for use witha wire arc spray system, the composite wire comprising: a low meltingpoint material at a core region thereof and a cladding including a metalsurrounding the core region, the low metal point material having amelting point less than that of the metal, wherein the low melting pointmaterial includes a polymer in the form of a powder having particleshaving a size of from approximately 1 nanometer to approximately 100nanometers.

A third aspect of the disclosure provides a method comprising:delivering a first all-metal wire to an arc point, the first all-metalwire having a first electrical polarity therein; delivering a secondall-metal wire to the arc point, the second all-metal wire having asecond electrical polarity therein that is opposite to the firstelectrical polarity; transmitting a propelling gas through the arc pointto propel heated material created by the arcing of the first all-metalwire and the second all-metal wire at the arc point to a surface to becoated; and controlling at least one of a voltage of the arc point, acurrent of the arc point, a volume of the propelling gas, a pressure ofthe propelling gas and a distance between the arc point and the surfaceto create a porous metal coating on the surface.

The illustrative aspects of the present disclosure are designed to solvethe problems herein described and/or other problems not discussed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this disclosure will be more readilyunderstood from the following detailed description of the variousaspects of the disclosure taken in conjunction with the accompanyingdrawings that depict various embodiments of the disclosure, in which:

FIG. 1 shows a schematic cross-sectional view of embodiments of a wirearc spray system according to the invention.

FIG. 2 shows a cross-sectional view of one embodiment of a compositewire according to the invention.

FIG. 3 shows a cross-sectional view of a second embodiment of acomposite wire according to the invention.

FIG. 4 shows a cross-sectional view of a third embodiment of a compositewire according to the invention.

FIG. 5 shows a flow diagram of a method according to embodiments of theinvention.

It is noted that the drawings of the disclosure are not to scale. Thedrawings are intended to depict only typical aspects of the disclosure,and therefore should not be considered as limiting the scope of thedisclosure. In the drawings, like numbering represents like elementsbetween the drawings.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, FIG. 1 shows a schematic cross-sectional viewof a wire arc spray system 100 according to embodiments of theinvention. While system 100 includes many features similar toconventional devices, wire(s) 102, 104 may be different thanconventional single material wires or conventional composite wires. Aswill be described in greater detail herein, wires 102, 104 allowcreation of a porous metal coating 124 on a surface 122 thatconventional wire arc spray systems are incapable of creating.

System 100 includes a propelling gas source 110 for delivering apropelling gas 112 to an arc point 114. Arc point 114 is a location atwhich wires 102, 104 come into contact and electrically arc based onelectric current therein, creating a heated material 120, which istransmitted to surface 122 by propelling gas 112. As used herein,“heated material” refers to material propelled toward surface 122, whichmay be simply heated and/or in any partial or wholly melted form. In oneembodiment, propelling gas 112 includes a compressed gas, e.g., argon,that propels heated material 120 from arc point 114 to surface 122 to becoated with porous metal coating 124. In this case, a source 116(indicated by an arrow) may include a tank of compressed gas. However,propelling gas 112 may also take the form of a combustion-based gas suchas may be created by a high velocity oxygen fuel (HVOF) process usinghydrogen gas or a liquid fuel like kerosene. Other combustion processesmay include, for example, combustion of oxygen and acetylene or oxygenand propylene. Typically, these combustion-based processes are not usedwith a wire arc spray system but rather with a powder material supplybecause the process does not provide adequate time to melt materialssufficiently to create a dense coating. In the present case, however, adense coating is not desirable. Consequently, a combustion-based gas maybe employed in a wire arc spray system. In this case, source 116 mayinclude a combustion chamber. Propelling gas source 110 may also includea nozzle 118 that may take any form now known or later developed todeliver propelling gas 112 in a manner appropriate for propelling heatedmaterial 120 to surface 122.

System 100 also may include a first wire delivery apparatus 130 fordelivering first wire 102 to arc point 114, and a second wire deliveryapparatus 132 for delivering second wire 104 to arc point 114. Althoughillustrated as simple tubular members with wire pulling pulleys,delivery apparatuses 130, 132 may take any now known or later developedstructure for delivering a wire or other rope-like structure to adesired location. For example, each apparatus 130, 132 may include anyvariety of guides, posts, reels, wheels, pulleys, motors, interactingwire grippers, etc., to move wires 102, 104 to arc point 114. A source140 of first wire 102 is positioned to provide the first wire to firstwire delivery apparatus 130, and a source 142 of second wire 104 ispositioned to provide the second wire to second wire delivery apparatus132. Sources 140, 142 may take any now known or later developed mannerof holding wire, e.g., a spool or reel.

System 100 also includes an electrical source 144 for creating a firstelectrical polarity, e.g., −, in first wire 102 and a second electricalpolarity, e.g., +, that is opposite to the first electrical polarity insecond wire 104. Each electrical polarity does not necessarily have toexhibit the same voltage and/or current. Electrical source 144 may becoupled to an end of each wire 102, 104 in any now known or laterdeveloped manner so as to create the requisite electrical polaritytherein, e.g., coupled to an internal end of each wire on a spool. It isalso understood that while one electrical source 144 is illustrated, twoelectrical sources, one for each wire, may also be employed.

System 100 also includes a controller 150 for controlling electricalsource 144, propelling gas source 110 and first and second wire deliveryapparatuses 130, 132 to propel heated and/or melted material 120 createdby the arcing of first wire 102 and second wire 104 at arc point 114 tosurface 122 to be coated. In addition, system 100 may include any nowknown or later developed mover(s) 152 for controlling a distance betweenarc point 114 and surface 122 to be coated such as a robotic arm, amotor, a mechanical linkage, etc. Controller 150 may control mover(s)152. Controller 150 may include any now known or later developedindustrial controller capable of the above-stated functions. Since suchcontrollers 150 are very well known in the art, no further descriptionis required.

Turning to FIGS. 2-4, details of first and second wires 102, 104 willnow be described. In one embodiment, one or both of first wire 102 andsecond wire 104 may include a composite wire 160 including a firstmaterial 162 at a core region thereof and a cladding including a secondmaterial 164 surrounding core region 162. Where only one wire 102, 104includes a composite wire, the other wire is an all-metal wire. In oneembodiment, first material 162 includes a low melting point materialhaving a melting point less than that of second material 164. Forexample, in one embodiment, as shown in FIG. 2, first material 162 mayinclude a polymer and second material 164 may include a metal. Forexample, first material 162 may include a polyester, and the metal maybe one or more of nickel and cobalt. In another embodiment, shown inFIG. 3, the polyester includes a powder having particles 166 having asize of approximately 1 nanometer to approximately 100 nanometers. Inanother example, first material 162 may include a relatively low meltingpoint metal such as aluminum, zinc or tin, and second material 164 mayinclude a higher melting point material such as nickel, cobalt and/orother higher melting point metals. The melting point of the listedmaterials are approximately as follows: aluminum 660° C., zinc 419° C.,tin 232° C., nickel 1453° C. and cobalt 1495° C. The melting point ofpolyester varies depending on the chemical formulation thereof, but islower than the second materials' listed above. In an alternativeembodiment, shown in FIG. 4, first material 162 may include a metal andsecond material 164 may include a polymer, such as those listed above.

In operation, wires 102, 104 are heated at arc point 114 and first andsecond materials 162, 164 are heated to melt at least a substantialportion of wires 102, 104 such that the heated material 120 istransmitted to surface 122 by propelling gas 112. Subsequently, surface122 can be heat treated at a high temperature (range dependent onmaterial to be removed) to melt or vaporize any remaining first material162 out of coating 124, leaving a porous coating of second material 164.For example, a temperature of approximately 1000° C. may be used tovaporize aluminum but leave a porous nickel. The porosity of coating 124can be determined by, for example, the diameter of first material 162,and process parameters used to deposit coating 124 such as, but notlimited to: a feed rate of wire(s) 102, 104, a distance between arcpoint 114 and surface 122, and propelling gas 112 flow volume andpressure. In addition, porosity can be controlled by the chemistry ofwire(s) 102, 104, which can be modified in terms of constituents andinternal core region pattern to produce a reproducible abradable coatingfor both high and low temperature applications.

Referring to the flow diagram of FIG. 5 in conjunction with FIG. 1, inother embodiments according to the invention, wire arc spray system 100may be employed using all-metal wires 202, 204 to create a porousabradable coating 124. In particular, in a process P10, first wiredelivery apparatus 130 delivers a first all-metal wire 202 to arc point114, and in process P12, second wire delivery apparatus 132 delivers asecond all-metal wire 204 to arc point 114. First all-metal wire 202 hasa first electrical polarity therein and second all-metal wire 204 has asecond electrical polarity therein that is opposite to the firstelectrical polarity, i.e., as created by electrical source 144. Inprocess P14, propelling gas source 110 transmits propelling gas 112through arc point 114 to propel heated and/or melted material 120created by the arcing of first all-metal wire 202 and second all-metalwire 204 at arc point 114 to surface 122 to be coated. However, incontrast to conventional wire arc spraying, controller 150 controls atleast one of a voltage of arc point 114, a current of arc point 114, avolume of propelling gas 112, a pressure of propelling gas 112 and adistance between arc point 114 and surface 122 to create a porous metalcoating 124 on surface 122. Voltage and current of arc point 114 may becontrolled via electrical source 144. Volume and pressure of propellinggas 112 may be controlled, for example, by valving in the case where thegas is compressed gas, by controlling the combustion process in the casewhere the gas is created from a combustion process or by othermechanisms known in the art. A distance of arc point 114 from surface122 can be controlled by mover(s) 152. A porosity of coating 124 can bedetermined by, for example, the types of metals used, the diameter offirst material (metal) 162, and the process parameters used to depositcoating 124 such as, but not limited to: a feed rate of wire(s) 202,204, a distance between arc point 114 and surface 122, and propellinggas 112 flow volume and pressure. In any event, this approach relies onwire arc system 100 having a very low velocity and ability to producelarge molten droplets that will produce porous coating 124. Oneillustrative application uses a nickel (Ni) wire and an aluminum (Al)wire, and the resulting coating would be a Ni matrix, NiAl (hard)inter-metallic particles, formed during the arc, with soft Al regions.Some abradable embodiments may include a hard phase to serve to “cut”the ductile coating in a rub/abrasion event.

An advantage that may be realized in the practice of some embodiments ofthe described systems and techniques is that composite wire 160 offers alower cost, more reproducible process to apply abradable coatings thatis also portable for field use as well as in the factory or service shopcompared to conventional composite powder spray systems. In addition,wire is less expensive to manufacture (perhaps ⅔ the cost), is moreportable and is more consistent and reproducible than metal/polymerpowder blends. Thus, coating 124 can be more reliably applied. In theFIG. 5 embodiment, the elimination of the need to perform a post coatingburn-out, a step currently used with the plasma spray processes and theFIGS. 2-4 embodiments, reduces feedstock costs and reduces time requiredto produce coating 124.

The foregoing drawings show some of the processing associated accordingto several embodiments of this disclosure. In this regard, each drawingor block within a flow diagram of the drawings represents a processassociated with embodiments of the method described. It should also benoted that in some alternative implementations, the acts noted in thedrawings or blocks may occur out of the order noted in the figure or,for example, may in fact be executed substantially concurrently or inthe reverse order, depending upon the act involved. Also, one ofordinary skill in the art will recognize that additional blocks thatdescribe the processing may be added.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present disclosure has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the disclosure in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the disclosure. Theembodiment was chosen and described in order to best explain theprinciples of the disclosure and the practical application, and toenable others of ordinary skill in the art to understand the disclosurefor various embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A wire arc spray system comprising: a compositewire including a core region having a first material and a claddingsurrounding the core region, wherein the cladding includes a metal, andthe first material includes a polymer; a first wire delivery apparatusphysically connected to the composite wire and configured to deliver thecomposite wire to an arc point; a second wire delivery apparatusconfigured to deliver a non-composite wire to the arc point; apropelling gas source for delivering a propelling gas to the arc point;an electrical source configured to create a first electrical polarity inthe composite wire and a second electrical polarity in the non-compositewire, the second electrical polarity being opposite to the firstelectrical polarity; a mover adapted to control a distance between thearc point and a surface to be coated; and a controller configured toprovide instructions to at least one of the mover, the electricalsource, the propelling gas source and the first and second wire deliveryapparatuses to propel molten droplets of a heated material on to thesurface to be coated, wherein the heated material is created by anarcing of the composite wire and the non-composite wire at the arcpoint, and wherein the propelling of the molten droplets of the heatedmaterial creates a porous metal coating on the surface to be coated. 2.The wire arc spray system of claim 1, wherein the controller is furtherconfigured to provide instructions to substantially vaporize the polymerby adjusting at least one of: a voltage level at the arc point, acurrent level at the arc point, a volume of the propelling gas, apressure of the propelling gas, a feed rate of the composite wire, afeed rate of the non-composite wire, and the distance between the arcpoint and the surface to be coated.
 3. The wire arc spray system ofclaim 1, wherein the non-composite wire is a metal wire and the firstmaterial further includes a polyester in the form of a powder havingparticles having a size of approximately 1 nanometer to approximately100 nanometers.
 4. The wire arc spray system of claim 3, wherein thepropelling gas is a combustion-based gas.
 5. The wire arc spray systemof claim 4, wherein the propelling gas source includes a combustionchamber.
 6. The wire arc spray system of claim 5, wherein the controlleris further configured to adjust a volume and a pressure of thepropelling gas flow by controlling a combustion process in thecombustion chamber.
 7. The wire arc spray system of claim 4, wherein thecombustion-based gas further includes a gas selected from the groupconsisting of: hydrogen, oxygen, acetylene, propylene, and kerosene. 8.The wire arc spray system of claim 1, wherein the first material furtherincludes a metal selected from the group consisting of: aluminum, zinc,and tin.
 9. The wire arc spray system of claim 1, wherein the controlleris further configured to provide instructions to control a porosity ofthe metal coating by adjusting at least one of: a voltage level at thearc point, a current level at the arc point, a volume of the propellinggas, a pressure of the propelling gas, a feed rate of the compositewire, a feed rate of the non-composite wire, and the distance betweenthe arc point and the surface to be coated.
 10. The wire arc spraysystem of claim 1, wherein the core region is configured in a patternadapted to provide the porous metal coating.
 11. The wire arc spraysystem of claim 1, wherein the polymer has a low melting temperaturerelative to the cladding and the non-composite wire.
 12. The wire arcspray system of claim 1, wherein the first material is a solid.